Cal. Sts. & High. Code § 30306

The money remaining in each separate toll revenue fund, after providing the amount required for interest and redemption of bonds, shall be held and applied as provided in the proceedings authorizing the issuance of the bonds. If the proceedings authorizing the issuance of the bonds do not require surplus revenues to be held or applied in any particular manner, they shall be allocated and used for other purposes incidental to the acquisition, construction, operation, and maintenance of the particular toll bridge or other highway crossing, transportation facilities, or additional transportation facilities as the commission determines.